Glycosphingolipids (GSLs) are a class of naturally occurring compounds which have a multitude of biological functions, including the ability to promote cell growth, cell differentiation, adhesion between cells or between cells and matrix proteins, binding of microorganisms and viruses to cells, and metastasis of tumor cells. GSLs are derived from glucosylceramide (GlcCer), which is produced from ceramide and UDP-glucose by the enzyme UDP-glucose: N-acylsphingosine glucosyltransferase (GlcCer synthase). The structure of ceramide is shown below: 
The accumulation of GSLs has been linked to a number of diseases, including Tay-Sachs, Gaucher""s, and Fabry diseases (see, for example, U.S. Pat. No. 6,051,598). GSLs have also been linked to certain cancers. For example, it has been found that certain GSLs occur only in tumors or at abnormally high concentrations in tumors; exert marked stimulatory or inhibitory actions on tumor growth when added to tumor cells in culture media; and inhibit the body""s normal immunodefense system when shed by tumors into the surrounding extracellular fluid. The composition of a tumor""s GSLs changes as the tumors become increasingly malignant and antibodies to certain GSLs inhibit the growth of tumors.
Compounds which inhibit GlcCer synthase can lower GSL concentrations and have been reported to be useful for treating subjects with one of the aforementioned diseases. A number of potent inhibitors of GlcCer, referred to herein as xe2x80x9cceramide-like compoundsxe2x80x9d, are disclosed in U.S. Pat. Nos. 6,051,598, 5,952,370, 5,945,442, 5,916,911 and 6,030,995. The term xe2x80x9cceramide-like compoundsxe2x80x9d refers to analogs of ceramide in which: 1) the primary alcohol is replaced with a substituted amino group; and 2) the alkenyl group (C13H27xe2x80x94CHxe2x95x90CHxe2x80x94) is replaced with an aryl group, preferably phenyl or substituted phenyl. An enantiomer of a ceramide-like compound is referred to here as a xe2x80x9cceramide-like enantiomerxe2x80x9d. The corresponding N-deacylated compounds are referred to as xe2x80x9csphingosine-like compoundsxe2x80x9d.
Unfortunately, known methods of preparing ceramide-like compounds are poorly suited for manufacturing on an industrial scale. Because of the two chiral centers, most known syntheses generate four diastereoisomers, resulting in the need to separate diastereomers by chromatography. Unfortunately, chromatography is generally poorly suited for large scale preparations. Thus, there is a critical need for diastereoselective syntheses of ceramide-like compounds which are more economical and involve fewer steps than known syntheses.
Reported herein is an efficient, highly diastereoselective synthesis of ceramide-like compounds. This synthesis of ceramide-like compounds involves only five steps from known compounds. For example, the ceramide-like compound designated xe2x80x9c(6)xe2x80x9d in FIG. 1 was produced in a diastereomeric excess of at least 99.3% and an overall yield of 16% (see Examples 1-5). Based on this discovery, novel reactions which can be used in a total synthesis of ceramide-like compounds and novel intermediates prepared by said reactions are disclosed herein.
One embodiment of the present invention is a method of preparing a first composition comprising a compound represented Structural Formula (I): 
The method comprises the step of reacting an aldehyde compound R10CHO with an isonitrile compound represented by Structural Formula (II): 
The reaction is carried out in the absence of a chiral inducing agent.
Another embodiment of the present invention is a method of preparing a second composition comprising a compound represented by Structural Formula (III): 
The second composition is prepared by hydrolyzing the oxazoline group in the compound represented by Structural Formula (I).
Another embodiment of the present invention is a method of preparing a third composition comprising a compound represented by Structural Formula (IV): 
The third composition is prepared by reacting the amide group in the compound represented by Structural Formula (III) with an amide reducing agent.
Another embodiment of the present invention is a method of preparing a fourth composition comprising a ceramide-like compound represented by Structural Formula (V): 
The fourth composition is prepared by acylating the free primary amine groups in the compound represented by Structural Formula (IV).
In Structural Formulas (I)-(V), R7 is an aliphatic group, preferably a C1-C30 straight chained alkyl or alkenyl group, more preferably a C8-C18 straight chained alkyl group; R10 is a substituted or unsubstituted aromatic group; and R20 and R30 are independently xe2x80x94H, a substituted or unsubstituted aliphatic group or, taken together with the nitrogen atom to which they are bonded, are a substituted or unsubstituted non-aromatic heterocyclic ring. Preferably, R10 is not 3-pyridyl, phenyl or 4-nitrophenyl when R20 and R30 are both xe2x80x94H.
Another embodiment of the present invention is a compound represented by Structural Formula (VI): 
R11 is a substituted or unsubstituted phenyl group. Examples of suitable substituents for the phenyl group represented by R11 include xe2x80x94OCH2Oxe2x80x94, xe2x80x94OCH2CH2Oxe2x80x94, halo, xe2x80x94O(lower alkyl), lower alkyl thiol, xe2x80x94OH, xe2x80x94O(phenyl), xe2x80x94Oxe2x80x94CH2-(phenyl), lower alkyl, amino, lower alkyl amino and lower dialkyl amino. In a preferred embodiment, the compound is Intermediate (3) depicted in FIG 1.
Yet another embodiment of the present invention is a compound represented by Structural Formula (VII): 
R12 is a phenyl group substituted with xe2x80x94OCH2CH2Oxe2x80x94, halo, xe2x80x94OH, (lower alkyl), lower alkyl thiol, xe2x80x94O(phenyl), xe2x80x94OCH2-(phenyl), lower alkyl, amino, lower alkyl amino and lower dialkyl amino. In a preferred embodiment, the compound is Intermediate (4) depicted in FIG. 1.
Also included in the present invention is the enantiomer of the compound represented by Structural Formula (VI) or (VII), mixtures of the compound and its enantiomer (including racemic mixtures), salts of each enantiomer and mixtures of salts of each enantiomer.
The reactions described above can be combined, resulting in an efficient and highly diastereoselective total synthesis of ceramide-like compounds. The compositions formed by each reaction is a racemic mixture. The ceramide-like enantiomers can be separated or resolved by standard methods of enantiomer separation known to one of ordinary skill in the art, thereby resulting in the preparation of an enantionmerically pure ceramide-like compound. Alternatively, an enantiomerically pure ceramide-like compound can be prepared by separating the enantiomers of the first, second or third racemic mixture and then completing the total synthesis with one or the other pure enantiomer from the first, second or third racemic mixture. Thus, the present invention contemplates performing each reaction with a racemic mixture or, alternatively, with an optically pure stereoisomer. The reactions depicted herein can alternatively be carried out with pure enantiomer or substantially pure enantiomer to yield an optically pure or substantially optically pure product.